1. Field of the Invention (Technical Field)
The present invention relates to air intake systems for air-breathing missiles, aircraft, and the like.
2. Description of Related Art
Volume constraints inside an air breathing missile or aircraft, combined with high inlet performance demands (i.e., high levels of total pressure recoveries and low distortion levels at the engine face) makes the integration and packaging of an air induction system a challenging problem. Significant compromises on inlet performance, and therefore on vehicle performance, are frequently made. It can be shown, both mathematically and experimentally, that engine thrust is directly proportional to inlet total pressure recovery.
Air breathing engines require flow from an inlet that minimizes losses and fits within the volume or packaging constraints. The size of the inlet capture and throat areas is dictated by the amount of air the engine, such as a turbojet, a turbofan or an auxiliary power unit, requires. Inlet capture and throat area requirements often compete with both internal and external physical and geometric constraints. Virtually all air-breathing missiles or aircraft work to these design constraints.
There are basically two types of prior art high performance subsonic inlets for missiles and aircraft, a pitot (or scoop) inlet, and a flush (or submerged) inlet.
Pitot or scoop inlets 10 (see FIGS. 1 and 2) generally exhibit better performance than flush inlets (when used in conjunction with boundary layer diverter 12) and capture more high energy air. Pitot or scoop inlets are advantageous because the boundary layer diverter precludes the ingestion of low momentum flow by the engine. The ingestion of high momentum air translates into improved inlet performance. The main disadvantage of pitot inlets is that the scoop significantly protrudes from the body's Outer Mold Line (OML). These protrusions can have significant effects on aerodynamic drag and moments (ΔCD and ΔCM). In addition, these protrusions can also adversely affect the vehicle's radar cross section.
Flush inlets 20 (see FIGS. 3, 4(a), and 4(b)) include an aperture that is submerged within the general contour of the fuselage and is approached by a long, gently-sloping ramp. Diverging sidewalls on the ramp cut across the streamlines, generating vortices, which energizes the flow.
The present invention combines the best attributes of a pitot (or scoop) inlet of FIGS. 1-2, with the best attributes of a submerged (or flush) type inlet of FIGS. 3-4. The hybrid air intake system retains the advantage of minimal protrusion from the fuselage of a submerged or flush inlet, while exhibiting the improved performance of a pitot or scoop inlet, that captures “clean” (i.e., boundary layer free) free stream air.